This invention relates to flywheel alternators used in conjunction with electronic ignition systems in internal combustion engines.
Basically, the alternator's function is to transform mechanical motion of the engine into electrical power. In the past, generated electricity was used solely to charge the ignition coil and activate electrical appliances. With the advent of spark ignited electronic ignition systems, a means was sought to modify the basic alternator so that it would generate a suitable ignition trigger pulse as well as perofrm its previous function. Proper engine performance requires a non-ambiguous uniquely defined pulse. In 2-stroke-cycle, 2 cylinder engines, for example, a precise firing pulse for each cylinder is required exactly once per engine revolution.
Conventional alternators, such as shown in U.S. Pat. No. 3,741,186, cause a voltage to be induced across a coil of conductive wire which is stationed in a rotating magnetic field. The field is produced within a cup shaped rotor which has permanent magnets circumferentially located in its inner diameter. The magnets have one of their two poles facing the rotor's center. Adjoining magnets have opposite polarity poles so oriented. The rotor is mechanically coupled to the engine and, when rotated, creates a time varying magnetic field within the rotor's diameter.
A cylindrical coil of conductive wire is stationed within the rotor in such a manner that the pole faces of the magnets form magnetic circuits with the poles of the coil. An alternating voltage is created across the coil as it is sequentially coupled to opposite magnetic fields. External circuitry rectifies the alternating voltage making it suitable for powering the ignition coil and other automotive appliances.
One method of modifying the conventional alternator to generate a trigger pulse is disclosed in U.S. Pat. No. 3,746,901 entitled "Magneto Generator For Ignition Systems of Internal Combustion Engines" issued on July 17, 1973. According to the invention, a reversely polarized control magnet is located within a main magnet. Pole shoes of a pulse generator winding are stationed to form a magnetic circuit when opposite the main magnet having the inner control magnet. At this time, a pulse is generated. An obvious disadvantage of this approach is that a special main and control magnet must be manufactured distinctly from the other main magnets.
S.A.E. paper 680579 published by T. Frazer Charmichael discloses a trigger circuit in which the south oriented main magnet of a conventional generator is replaced with a north oriented magnet. This results in three adjoining north polarity main magnets. Two trigger coils are positioned on adjacent salient poles. As the trigger coils are wired in opposition, there will be no net voltage developed across them until each is opposite the same polarity magnetic pole. However, since there are three adjacent north oriented poles, this system will produce two pulses per revolution. This may result in engine misfiring.
Accordingly it is an object of this invention to provide a new and improved flywheel alternator for use with a pulse triggered ignition system which produces a single trigger pulse suitable for triggering an electronic ignition system each engine revolution.
It is another object of the invention to provide a flywheel alternator of the type described in the previous paragraph having a single trigger coil.
It is a further object of the invention to provide a flywheel alternator as above-described which uses main magnets all of which have similar manufacture.